Energization control device for electric motors

Abstract

An energization control device is provided to prevent rapid decrease of current which is flowing through each of phase coils of an electric motor. A time duration is divided into three stages which ranges from an initiation of the current supply to the phase coil to a termination of the current supply to the phase coil. At the first stage, the second stage, and the third stage, soft/hard chopping energization control, 0-volt energization, and duty chopping energization control, respectively, are made. Energizing the phase coil is made by way of a first switching element and a second switching element. At the first stage, depending on an actual current value being in excess of a target current value, either of or both of the first switching element and the second element are made OFF. At the second stage, while the second switching element is being made OFF, the second switching element is made ON. At third stage, while the second switching element is being made OFF, the first switching element is, at a duty cycle, made ON and OFF alternately in repetition.

What is claimed is:  
     
       1. An energization control device for electric motors comprising: 
       a plurality of phase coils arranged on a stator, one end of each of the phase coils being connected to one of high and low potential lines of a power supply by way of a first switching element,  
       the other end of each of the phase coils being connected to the other of the high and low potential lines of the power supply by way of a second switching element,  
       one end of the each of the phase coils being connected to the other of the high and low potential lines of the power supply by way of a first diode which allows current flow from the latter to the former,  
       the other end of each of the phase coils being connected to one of the high and low potential lines of the power supply by way of a second diode which allows current flow from the former to the latter; angular position detection means for detecting an angular position of the rotor;  
       rotational speed detection means for detecting a rotational speed of the rotor;  
       actual current detection means for detecting an actual current which passes through each of the phase coils; and  
       control means determining an energization-on angle, a first energization-off angle and a target current value, for each of the phase coils, on the basis of the rotational speed of the rotor and a target torque which is calculated based on an external information inputted,  
       the control means making one of the first and second switching elements ON-OFF and the other ON while the rotor rotates from the energization-on angle to the first energization-off angle, and approximating the actual current value to the target current value,  
       the control means determining a second energization-off angle on the basis of the target torque and the rotational speed of the rotor for each of the phase coils,  
       the control means making both the first and second switching elements OFF concurrently while the rotor rotates from the second energization-off angle to the energization-on angle,  
       the control means making one of the first and second switching elements ON-OFF at an arbitrary duty ratio and making the other OFF while the rotor moves from the first energization-off angle to the second energization-off angle.  
     
     
       2. An energization control device as set forth in  claim 1 , wherein the control means determines an intermediate energization-off angle between the first energization-off angle and the second energization-off angle, holds a condition under which one of the first and second switching elements is made ON and the other is made OFF concurrently while the rotor rotates from the first energization-off angle to the intermediate energization-off angle, and makes one of the first and second switching elements ON-OFF at an arbitrary duty ratio and makes the other OFF while the rotor moves from the intermediate energization-off angle to the second energization-off angle. 
     
     
       3. An energization control device as set forth in  claim 2 , wherein the control means makes one of the first and second switching elements ON-OFF at the duty ratio which is changed such that a ratio of an ON-time duration to an OFF-time duration is reduced with passing of time and makes the other OFF while the rotor moves from either of the first energization-off angle or the intermediate energization-off angle to the second energization-off angle. 
     
     
       4. An energization control device as set forth in  claim 3 , wherein either the first energization-off angle or the intermediate energization-off angle which are originally determined is put ahead. 
     
     
       5. An energization control device as set forth in  claim 4 , wherein between the first energization-off angle to the intermediate energization-off angle, the target current value is increased.